1. Field of the Invention
This invention relates to a light receiving member such as electrophotographic photosensitive member, etc., and a process for forming an image on it, and more particularly to a light receiving member suitable for an electrophotographic printer of a type of line-scanning a laser beam on an image pattern and a process for forming an image on it.
2. Description of the Prior Art
Electrophotographic printers of a type of line-scanning a laser beam have heretofore utilized gas lasers of relatively short wavelength such as helium-cadmium laser, argon laser, helium-neon laser, etc. as laser beam. A CdS-binder-based photosensitive layer having a thick photosensitive layer, and a charge transfer complex [IBM Journal of the Research and Development, January (1971), pages 75-89] have been also utilized as an electrophotographic photosensitive member. Thus, the laser beam undergoes no multiple reflection in the photosensitive layer with the result that no image of interference fringe pattern actually appears during the image formation.
In the meantime, a semi-conductor laser has been recently utilized in place of the gas laser to produce the devices on a smaller scale and at a lower cost. The semi-conductor laser generally has an oscillation wavelength in a longer wavelength region such as 750 nm or more, and thus an electrophotographic photosensitive member having a high sensitivity characteristic in the longer wavelength region have been needed, and consequently research and development of electrophotographic photosensitive members having such sensitivity characteristic have been so far made.
So far known photosensitive members having a photosensitivity to light of longer wavelength, for example. 600 nm or more, include, for example, a lamination type electrophotographic photosensitive member having a layer structure comprising a charge transport layer and a charge generation layer containing phthalocyanine pigments such as copper phthalocyanine, aluminum chloride phthalocyanine, etc., and also an electrophotographic photosensitive member using a selenium-tellurium film.
When such a photosensitive member having a photosensitivity to light of longer wavelength is subjected to laser beam exposure on an electrophotographic printer of laser beam scanning type, an interference fringe pattern appears on the formed toner image and no good reproduction image can be obtained. One of causes for these disadvantageous phenomena seems to be that the longer wavelength laser is not completely absorbed in the photosensitive layer and the transmitted light undergoes normal reflection on the substrate surface, generating multiple reflections of the laser beam in the photosensitive layer, and causing an interference between the reflected light on the photosensitive layer surface and the multiple reflections.
To eliminate multiple reflections generated in the photosensitive layer to overcome the disadvantages, a method for roughening the surface of electroconductive substrate used in the electrophotographic photosensitive member by anodic oxidation or by sand blasting, a method for providing a light-absorbing layer or a reflection-preventing layer between the photosensitive layer and the substrate, etc. have been so far proposed, but actually the interference fringe pattern appearing during the image formation cannot be completely eliminated. Particularly according to the method for roughening the surface of electroconductive substrate it is hard to form a roughened surface with uniform roughness, and sites with relatively large roughness may be sometimes formed to some degree. These sites with relatively large roughness may act as carrier injection ports into the photosensitive layer, generating white dots during the image formation or black dots when the reversal development system is used. Thus, the surface-roughening method is not preferable. Furthermore, it is difficult to produce electroconductive substrates with uniform roughness in one lot during the production and thus the method still has many improvements. Even according to the method using a light-absorbing layer or a reflection-preventing layer, the interference fringe pattern cannot be thoroughly eliminated, and furthermore there are disadvantages of increased production cost, etc.